Ceramic powder and multi-layer ceramic capacitor

ABSTRACT

A ceramic powder that contains, as a main composition, barium titanate powder having a perovskite structure with an average particle size (median size) of 200 nm or smaller as measured by SEM observation, wherein the the barium titanate powder is such that the percentage of barium titanate particle having twin defects in the barium titanate powder is less than 10% as measured by TEM observation and that its crystal lattice c/a is 1.0075 or more. The ceramic powder is particularly useful in the formation of thin dielectric layers of 1 μm or less and can be used to manufacture MLCCs having both desired capacity and longevity traits.

BACKGROUND

1. Field of the Invention

The present invention relates to a ceramic powder that contains bariumtitanate having a perovskite structure, and a multi-layer ceramiccapacitor (MLCC) obtained by using said ceramic powder, particularlyuseful for a MLCC using a thin-layer dielectric layer.

2. Description of the Related Art

Multi-layer ceramic capacitors (MLCCs) are used in various electronicdevices including mobile devices and communications devices.

The trend for smaller, higher-performance MLCCs and other electroniccomponents has been prominent in recent years and, in the case of MLCCs,for example, these capacitors are becoming significantly smaller andlarger in capacity. The capacity of a MLCC is proportional to the numberof dielectric layers constituting the base material of the MLCC, andinversely proportional to the thickness per dielectric layer, andconsequently it is desirable to keep the dielectric layer thin, such as1 μm or less, and increase the number of layers.

For the material ceramic powder with which to form such dielectriclayer, barium titanate powder having a perovskite structure is widelyused.

To ensure performance and reliability, and also from the viewpoint ofphysical characteristics, it is important that the barium titanatepowder consist of fine particles so as to make the aforementioneddielectric layer thinner.

According to Patent Literature 1, the powder of barium titanate compoundobtained by the method described therein has an average particle size of100 nm or smaller, contains twin defects in at least 10% of theparticles, and its standard deviation of particle size distribution is20 or less.

BACKGROUND ART LITERATURE Patent Literature

[Patent Literature 1] Japanese Patent Laid-open No. 2011-132071

SUMMARY

However, although making ceramic powder finer, as is the case with theceramic powder obtained according to the method described in PatentLiterature 1, increases the number of grain-boundary particles perdielectric layer that play an important role in the longevity traits ofthe MLCC and thereby improves the longevity traits of the MLCC, finerceramic powder means greater surface area and lower dielectric constant(sizing effect of barium titanate).

This means that, in order to obtain the same capacitance that can beachieved with powder of normal particle size, the thickness of thedielectric layer must be reduced, and as a result the DC electric fieldapplied per the unit thickness of dielectric layer rises and thelongevity traits of the MLCC worsens. This gives rise to a need forMLCCs offering desired capacity and longevity traits at the same time.

Accordingly, an object of the present invention is to provide a ceramicpowder whose main ingredient is barium titanate having a perovskitestructure, wherein said powder is particularly useful in the formationof thin dielectric layers of 1 μm or less and can be used to manufactureMLCCs having both desired capacity and longevity traits, so that MLCCproducts offering excellent capacity and longevity traits can beprovided.

The inventor of the present invention completed the present inventionafter discovering that such problems could be resolved by a ceramicpowder which has a specific average particle size or smaller, exhibitstwin defects by less than a specific percentage, and contains bariumtitanate of high tetragonality whose crystal lattice c/a is at or abovea specific value.

In other words, the present invention is a ceramic powder that containsbarium titanate having a perovskite structure, with an average particlesize (median size) of 200 nm or smaller as measured by SEM observation,wherein said ceramic powder is such that the percentage of twin defectsin the barium titanate is less than 10% as measured by TEM observationand that its crystal lattice c/a is 1.0075 or more.

Preferably the barium titanate has a percentage of twin defects of 5 to9%, crystal lattice c/a of 1.0075 to 1.0104, and average particle sizeof 80 to 150 nm. By using the ceramic powder proposed by the presentinvention, which meets the above ranges, MLCCs offering excellentcapacity and longevity traits can be produced.

Furthermore, the MLCC proposed by the present invention is made byalternately layering a dielectric layer constituted by a sintered bodyof the ceramic powder proposed by the present invention, and an internalelectrode layer.

According to the present invention, a ceramic powder is provided whosemain ingredient is barium titanate, wherein said powder is particularlyuseful in the formation of thin dielectric layers of 1 μm or less andcan be used to manufacture MLCCs having both desired capacity andlongevity traits, so that MLCC products offering excellent capacity andlongevity traits can be provided by using this ceramic powder.

Any discussion of problems and solutions involved in the related art hasbeen included in this disclosure solely for the purposes of providing acontext for the present invention, and should not be taken as anadmission that any or all of the discussion were known at the time theinvention was made.

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1 is a simple drawing showing a barium titanate particle in whichtwin defects are formed.

FIG. 2 is a schematic longitudinal cross-section view of a multi-layerceramic capacitor conforming to the present invention.

DESCRIPTION OF THE SYMBOLS

1 Multi-layer ceramic capacitor

10 Ceramic sintered body

11 Laminate

12 Dielectric layer

13 Internal electrode layer

15 Cover layer

20 External electrode

DETAILED DESCRIPTION OF EMBODIMENTS

As mentioned above, the ceramic powder proposed by the present inventioncontains barium titanate having a perovskite structure, and the averageparticle size (median size) of the barium titanate as measured byobservation using a scanning electron microscope (SEM) is 200 nm orless. The particle size can be the maximum width of the particleobserved with SEM. The median size is the particle size of the medianparticle (d50) when counting particles in the order of the size.

The aforementioned average particle size can be obtained by observing apowder sample of barium titanate using a SEM wherein n=500 (measuring500 particles), and then taking the median size of the measuredparticles. The 500 particles can be selected randomly or can be all theparticles observed in a randomly selected region or regions.

If the average particle size is 200 nm or larger, a smooth and highlyreliable dielectric layer of 1 μm or less in thickness cannot beobtained.

Additionally, the average particle size is normally 80 nm or more, orpreferably 80 to 150 nm from the viewpoint of obtaining a thindielectric layer. How to adjust the average particle size will bedescribed later.

Next, the aforementioned barium titanate having a perovskite structurehas a percentage of twin defects, as measured by observation using atransmission electron microscope (TEM), of less than 10%. The percentageof twin defects is measured by observing a powder of the barium titanateusing a TEM and counting, among 100 particles (n=100 wherein the 100particles can be selected randomly or can be all the particles observedin a randomly selected region or regions), those particles in which twindefects are formed. FIG. 1 shows a schematic drawing of a bariumtitanate particle in which twin defects are formed (the right particlewith two lines).

From this viewpoint of achieving the intended effect of the presentinvention, preferably the aforementioned percentage of twin defects is 5to 9%. How to adjust the percentage of twin defects will be describedlater.

As mentioned above, the crystal lattice c/a of the barium titanatehaving a perovskite structure is 1.0075 or more. The c/a can be obtainedby measuring the diffraction peak of the barium titanate (as a bariumtitanate powder sample in its entirety) according to any known powderX-ray diffraction method, analyzing the obtained diffraction peakaccording to the Rietveld method, and then calculating the latticeconstants for axis a and axis c.

Such ceramic powder proposed by the present invention, having hightetragonality of barium titanate and a certain average particle size orsmaller, can achieve both desired dielectric constant and acceleratedlife and these characteristics can be used to manufacture MLCCs offeringexcellent capacity and longevity traits. In this disclosure, the“ceramic powder” contains the “barium titanate powder” as a main orpredominant composition, consists essentially of the “barium titanatepowder”, is characterized by the “barium titanate powder”, or isequivalent to the “barium titanate powder”.

From the above viewpoints, preferably the c/a is 1.0075 to 1.0104. Howto adjust the c/a will be described later.

Next, how to manufacture the ceramic powder proposed by the presentinvention is explained. The manufacturing method is not limited in anyway, so long as the barium titanate constituting the main ingredient ofthe powder meets the various parameters explained above. However, thepowder can be manufactured as described below by considering andadjusting the various conditions and factors, for example.

In general, titanium material and barium material are reacted with eachother to synthesize barium titanate, which is then heat-treated andsintered into a ceramic powder, after which the powder is crushed toadjust the particle size as necessary and, if necessary, the crushedpowder is further mixed with various additive compounds.

Various methods have been known to synthesize the aforementioned bariumtitanate, where examples include the sol-gel method, hydrothermalmethod, and solid phase method.

Among these methods, the sol-gel method and hydrothermal method tend tosuppress generation of twin defects and lower the c/a value.

The solid phase method tends to generate more twin defects and raise thec/a value.

To keep the percentage of twin defects at less than 10%, it isdesirable, under the present invention, to adopt the hydrothermalmethod.

In addition, the c/a value tends to rise if the ratio of barium andtitanium (Ba/Ti) in the synthesized barium titanate is slightly greaterthan the stoichiometric level, or it tends to drop if this ratio isslightly lower than the stoichiometric level. This ratio does not affectthe percentage of twin defects much.

Furthermore, under the present invention, preferably the aforementionedheat treatment is implemented in two separate stages of hydrothermaltreatment and heat treatment.

If the temperature or time of the aforementioned heat treatment ishigher or longer, the percentage of twin defect generation increases andthe c/a value tends to rise. Conversely if the temperature or time ofheat treatment is lower or shorter, generation of twin defects issuppressed and the c/a value tends to drop.

By adding heat treatment, barium titanate is sintered and the particlegrows in size, and consequently barium titanate powder having a desiredaverage particle size can be obtained. This heat treatment alsoincreases the percentage of twin defects in barium titanate as well asthe c/a value of its crystal lattice.

Conditions of the aforementioned heat treatment are not limited in anyway, but the heat treatment, normally, is performed under the conditionsof 500 to 1200° C. for 0.5 to 4 hours, or preferably under theconditions of 780 to 870° C. for 2 to 3 hours. This heat treatment maybe performed in atmosphere or in an ambience of N₂, etc.

By providing heat treatment at a specific temperature for a specifiedtime as mentioned above, the level of particle growth can be controlledand a desired average particle size can be achieved. While the averageparticle size of barium titanate powder is normally 10 to 85 nm beforesintering, this heat treatment (sintering) increases the size normallyto as much as 80 to 200 nm and makes the dielectric constant higher.

The heat treatment explained above adjusts the percentage of twindefects in barium titanate and raises the c/a value of crystal lattice.

The barium titanate that has undergone the aforementioned heat treatment(sintering) is then put through hydrothermal treatment. Thishydrothermal treatment is realized by introducing the aforementionedbarium titanate powder into water or specified aqueous solution or otherliquid and then adding thermal energy to the powder using the liquid asthe medium.

Preferably the hydrothermal treatment temperature is 100° C. or higher,because the tetragonality of barium titanate is not expected to increasemuch when this temperature is lower than 100° C. The hydrothermaltreatment temperature is normally 200° C. or lower.

The hydrothermal treatment time is not limited in any way, but at leastone hour of hydrothermal treatment is enough and normally the treatmenttime is 24 hours or less.

As for the pressure of hydrothermal treatment, sufficient effects can beexpected at a pressure of at least 1 MPa, and the pH of hydrothermaltreatment is normally 12 to 12.5.

In addition, while the liquid for hydrothermal treatment may be water,it is preferable to use an aqueous solution that contains A-site metalions of the aforementioned barium titanate having a perovskitestructure, or specifically barium ions, to a certain concentration, ordesirable to use an aqueous solution that contains A-site metal ions byat least 0.1 times the mole number of A-site metal contained in thepowder to be treated.

After the hydrothermal treatment, barium titanate powder is dried andthen crushed to adjust the particle size, as necessary, or crushing iscombined with classification to regulate the particle size.

This crushing can be done using either a wet method or dry method, butdry crushing is preferred from the viewpoint of drying cohesion. Note,however, that dry crushing tends to lower the c/a value. It does notaffect the percentage of twin defects much.

Under the present invention, individual conditions, etc., areadjusted/set as deemed appropriate, with an understanding of what eachof the above operations tends to do, to manufacture a barium titanatepowder having a perovskite structure and meeting the average particlesize, percentage of twin defects and c/a value as specified under thepresent invention.

Particularly under the present invention, it is preferable to obtain abarium titanate powder by: manufacturing barium titanate according tothe hydrothermal method; heat-treating the manufactured barium titanateunder the conditions of 500 to 1200° C. for 0.5 to 4 hours;hydrothermally treating the heat-treated barium titanate under theconditions of 100 to 200° C. for 1 to 24 hours at a pH of 12 to 12.5;and dry-crushing the hydrothermally treated barium titanate asnecessary.

The ceramic powder proposed by the present invention contains a bariumtitanate powder obtained in the manner described above, for example, andit also contains various additive compounds as necessary, as describedlater.

For example, the ceramic powder proposed by the present invention, beingobtained as explained above, has a small average particle size and thischaracteristic can be used to manufacture high-quality MLCCs having adielectric layer of 1 μm or less in thickness. Manufactured MLCCs havesufficient capacitance and offer excellent product longevity traits.

The ceramic powder proposed by the present invention contains a bariumtitanate powder obtained in the manner described above, for example, andit also contains various additive compounds as necessary, as describedlater.

For example, the ceramic powder proposed by the present invention, beingobtained as explained above, has a wide range of optimum sinteringtemperatures and a small average particle size, and thesecharacteristics can be used to manufacture, at a high yield,high-quality MLCCs having a dielectric layer of 1 μm or less inthickness. Manufactured MLCCs have sufficient capacitance, present lesscapacitance variation among individual products, and are resistant todefects.

Next, a multi-layer ceramic capacitor according to an embodiment of thepresent invention is explained. FIG. 2 is a schematic longitudinalcross-section view of a multi-layer ceramic capacitor 1 conforming tothe present invention.

The multi-layer ceramic capacitor 1 is generally constituted by aceramic sintered body 10 having standard chip dimensions and shape (suchas a rectangular solid of 1.0×0.5×0.5 mm), and a pair of externalelectrodes 20 formed on both sides of the ceramic sintered body 10. Theceramic sintered body 10, whose main ingredient is barium titanateparticle crystal, has a laminate 11 formed by alternately layeringdielectric layers 12 and internal electrode layers 13 inside, and coverlayers 15 formed as the outermost layers provided at the top and bottomin the laminating direction.

The laminate 11, where each dielectric layer 12 sandwiched by twointernal electrode layers 13 has a thickness of 1 μm or less (such asapprox. 900 nm) according to the specifications of capacitance andrequired pressure resistance, etc., has a high-density, multi-layerstructure comprising several dozen to several hundred layers in total.

The cover layers 15 formed as the outermost layers of the laminate 11protect the dielectric layers 12 and internal electrode layers 13 fromexternal contamination due to humidity, contaminants, etc., and preventdeterioration of these layers over time.

The multi-layer ceramic capacitor 1 is manufactured as follows, forexample. First, a material fine-particle powder whose main ingredient isbarium titanate is wet-mixed with additive compounds, after which themixture is dried and crushed to prepare a dielectric powder (ceramicpowder conforming to the present invention). Examples of the additivecompounds include oxides of Mg, Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Cr, V, Mn, Co, Ni, Nb, Ta, Mo, W, Si, Li, B, Na and K, among others.These additive compounds, normally, are added by 0.01 to 0.1 mol intotal, per 1 mol of barium titanate.

The prepared dielectric powder is wet-mixed using a binder such aspolyvinyl butyral resin, and an organic solvent such as ethanol, afterwhich the mixture is coated on a base material in a band form as adielectric green sheet of 1 μm or less in thickness according to thedie-coater method, doctor blade method, etc., and then dried. Next, ametal conductive paste containing organic binder is printed on thesurface of the dielectric green sheet by means of screen printing orgravure printing, to place an internal electrode layer 13 pattern. Forthe aforementioned metal, nickel is widely used from the viewpoint ofcost.

It is possible to uniformly disperse barium titanate with an averageparticle size of 50 nm or less, in the aforementioned metal conductivepaste, as a co-material. Thereafter, a specified number of dielectricgreen sheets, which have been stamped out to an identical size of 15cm×15 cm, for example, are layered so that the internal electrode layers13 and dielectric layers 12 alternate. Cover sheets that will becomecover layers 15 are then pressure-bonded at the top and bottom of thelayered dielectric green sheets, after which the laminate is cut tospecified chip dimensions (such as 1.0 mm×0.5 mm) and then a Niconductive paste that will form external electrodes 20 is coated on bothside faces of the laminate and dried. This way, a molding of multi-layerceramic capacitor 1 is obtained.

The molding of multi-layer ceramic capacitor 1 thus obtained is placedin a N₂ ambience of approx. 350° C. to remove the binder, and thensintered for 10 minutes to 2 hours at 1100 to 1280° C. under a mixed gascontaining N₂, H₂ and H₂O (whose oxygen partial pressure is approx.1.0×10⁻¹¹ MPa), to obtain a multi-layer ceramic capacitor 1.

In the obtained multi-layer ceramic capacitor 1, the internal electrodelayers 13 are embedded in such a way that their edges are exposedalternately at both end faces of the dielectric layers 12 in the lengthdirection, where the exposed edges of internal electrode layers 13 areconnected to the external electrodes 20.

Also, the thickness of the dielectric layer 12 is normally 3 μm or less,or preferably 0.5 to 1 μm, while the thickness of the internal electrodelayer 13 is normally 0.5 to 3 μm. With the ceramic powder proposed bythe present invention, the average particle size of its main ingredient,or specifically barium titanate, is controlled to 200 nm or less, andtherefore a surface of excellent smoothness can be achieved even on suchthin dielectric layer, and consequently a multi-layer ceramic capacitorresistant to shorting and other problems can be obtained.

Furthermore, the aforementioned sintering forms particles of acore-shell structure, where each particle has a core of barium titanatebeing the main ingredient of the aforementioned dielectric powder, and ashell constituted by the aforementioned additive compounds and solidsolution of barium titanate, and this structure adds favorabletemperature characteristics to the dielectric layer and keeps changes incapacitance and other performance-related characteristics to a minimumor none, even when the MLCC is subject to changing ambient temperatures.

EXAMPLES Example 1

A barium titanate powder having a perovskite structure was obtainedaccording to the method described below.

First, barium hydroxide salt was mixed into a slurry in which titaniumoxide particles of 50 nm in average particle size were dispersed, andthe mixture was put through hydrothermal reaction under the conditionsof 120° C. for 48 hours at a pH of 13, to obtain a barium titanatepowder.

Thereafter, this powder was heat-treated (sintered) under the conditionsof 800° C. for 3 hours in a N₂ ambience, and then the heat-treatedpowder was hydrothermally treated again under the conditions of 100° C.for 24 hours at a pH of 12. The obtained barium titanate had abarium-titanate (Ba/Ti) ratio of 1.0010, average particle size of 125nm, overall percentage of twin defects containing particles of 9%, andc/a of 1.0085.

As for the average particle size, a powder sample was observed using aSEM and sizes of 500 particles were measured, and the median size(diameter) was taken as the average particle size.

The percentage of twin defects was obtained by observing a powder sampleusing a TEM and counting, among 100 particles, those particles in whichtwin defects were formed.

Furthermore, the c/a was obtained by X-ray diffraction measurement ofpowder, followed by the Rietveld analysis.

The obtained barium titanate powder was used as the material to obtain aceramic powder based on a X7R dielectric composition{(100BaTiO₃-1.25Ho₂O₃-1.2MgO-0.25MnO₂-1.3SiO₂); the unit is mol}, afterwhich a MLCC molding was prepared using a normal method and thensintered in a sintering furnace in a N₂-based ambience of 0.75% in H₂concentration, at a sintering temperature of 1200° C., to prepare a MLCC(in the form of 1.0×1.0×0.5 mm) having 50 dielectric layers, 51 nickelinternal electrode layers, and thickness per dielectric layer of 1 μm.

When the prepared MLCC was evaluated for electrical characteristics(specific dielectric constant, dielectric loss and life), the specificdielectric constant (εγ) was 3250, dielectric loss (tans) was 3.50%, andmean time to failure during the accelerated longevity test was 560minutes (n=100).

The accelerated longevity test was conducted under the conditions of105° C. and E=50 V/μm. As for the relationship of specific dielectricconstant and life, the test result under these conditions was given a“Pass” (O) when the relationship of y≧10²⁰×x⁻⁵ was established, where yrepresents the mean time to failure and x represents the specificdielectric constant.

The above results are summarized in Tables 1 and 2 below. It should benoted that a TEM structural analysis of sintered MLCCs found that themeasured MLCCs contained twin defects at a percentage equivalent to thepercentage of twin defects in the material ceramic powder used in themanufacture thereof.

Comparative Example 1

Barium hydroxide salt was mixed into a slurry in which titanium oxideparticles of 50 nm in average particle size were dispersed, and themixture was put through hydrothermal reaction under the conditions of120° C. for 48 hours at a pH of 13, to obtain a barium titanate powder.

Thereafter, this barium titanate powder was heat-treated (sintered)under the conditions of 800° C. for 3 hours in a N₂ ambience, and thenthe sintered barium titanate powder was hydrothermally treated under theconditions of 100° C. for 24 hours at a pH of 12.

The obtained barium titanate was crushed using an air-jet type drycrusher (Jet Mill), to obtain a barium titanate powder. The obtainedbarium titanate had a barium-titanate (Ba/Ti) ratio of 1.0010, averageparticle size of 115 nm, overall percentage of twin defects containingparticles of 9%, and c/a of 1.0073.

This barium titanate powder was used as the material to prepare aceramic powder based on the same composition as in Example 1, which wasthen used to obtain a MLCC molding under a normal method, and theobtained molding was sintered in a sintering furnace under the sameconditions as in Example 1, to prepare a MLCC having 50 dielectriclayers, 51 nickel internal electrode layers and thickness per dielectriclayer of 1 μm. When the obtained MLCC was evaluated for electricalcharacteristics, the specific dielectric constant (εγ) was 3250,dielectric loss (tan δ) was 7.20%, and mean time to failure during theaccelerated longevity test was 260 minutes, indicating that the MLCC hadinsufficient longevity traits.

The above results are summarized in Tables 1 and 2 below. It should benoted that a TEM structural analysis of sintered MLCCs found that themeasured MLCCs contained twin defects at a percentage equivalent to thepercentage of twin defects in the material ceramic powder used in themanufacture thereof

Examples 2 to 6, Comparative Examples 2 to 5

Barium titanate powders were manufactured in the same manner as inExample 1, except that the hydrothermal reaction conditions in thesynthesis of barium titanate, average particle size before/after heattreatment, various heat treatment conditions, crushing conditions,barium-titanate (Ba/Ti) ratio, generation ratio of twin defects, and c/avalue, were changed as shown in Table 1 below.

The obtained barium titanate powder was used as the material to preparea ceramic powder based on the same composition as in Example 1, whichwas then used to obtain a MLCC molding under a normal method, and theobtained molding was sintered in a sintering furnace under the sameconditions as in Example 1, to prepare a MLCC having 51 nickel internalelectrode layers and thickness per dielectric layer of 1 μm. Theobtained MLCC was evaluated for electrical characteristics.

The results are shown in Table 2 below. It should be noted that, in allexamples, a TEM structural analysis of sintered MLCCs found that themeasured MLCCs contained twin defects at a percentage equivalent to thepercentage of twin defects in the material ceramic powder used in themanufacture thereof.

TABLE 1 Treatment Percentage Treatment [1] [2] Treatment [3] Average oftwin Material Hydrothermal Solid phase Hydrothermal Dry particle sizedefects Ti source reaction reaction treatment crushing Ba/Ti nm % c/aExample [1] TiO2/ 120° C./ 800° C./ 100° C./ None 1.0010 125 9% 1.008550 nm 48 hours/ 3 hours/ 24 hours/ pH of 13 N₂ pH of 12 ambienceComparative TiO2/ 120° C./ 800° C./ 100° C./ Performed 1.0010 115 9%1.0073 Example [1] 50 nm 48 hours/ 3 hours/ 24 hours/ pH of 13 N₂ pH of12 ambience Comparative TiO2/ 120° C./ 870° C./ 100° C./ None 0.9998 12012%  1.0078 Example [2] 45 nm 12 hours/ 3 hours/ 12 hours/ pH of 12 N₂pH of 12 ambience Comparative TiO2/ 120° C./ 870° C./ 100° C./ Performed0.9998 110 12%  1.0072 Example [3] 45 nm 12 hours/ 2 hours/ 12 hours/ pHof 12 N₂ pH of 12 ambience Example [2] TiO2/ 130° C./ 815° C./ 100° C./None 1.0015 150 5% 1.0091 85 nm 36 hours/ 2 hours/ 24 hours/ pH of 13.5N₂ pH of 12 ambience Example [3] TiO2/ 130° C./ 815° C./ 100° C./Performed 1.0008 135 5% 1.0075 85 nm 36 hours/ 2 hours/ 24 hours/ pH of13.5 N₂ pH of 12 ambience Example [4] TiO2/ 120° C./ 870° C./ 100° C./None 1.0005 200 7% 1.0104 80 nm 24 hours/ 2 hours/ 16 hours/ pH of 12.5atmosphere pH of 12.5 Example [5] TiO2/ 120° C./ 870° C./ 100° C./Performed 1.0003 190 7% 1.0092 80 nm 24 hours/ 2 hours/ 16 hours/ pH of12.5 atmosphere pH of 12.5 Example [6] TiO2/ 115° C./ 780° C./ 100° C./None 0.9998 95 7% 1.0082 10 nm 8 hours/ 3 hours/ 8 hours/ pH of 13.5atmosphere pH of 12.5 Comparative TiO2/ 115° C./ 780° C./ 100° C./Performed 0.9998 90 7% 1.0070 Example [4] 10 nm 8 hours/ 3 hours/ 8hours/ pH of 13.5 atmosphere pH of 12.5 Comparative TiO2/ 130° C./ 780°C./ 100° C./ None 0.9998 95 7% 1.0070 Example [5] 90 nm 36 hours/ 3hours/ 8 hours/ pH of 13.5 atmosphere pH of 12.5

A comparison of Example 1 and Comparative Example, for example, 1 showsthat crushing reduces the average particle size of barium titanatepowder and also reduces the c/a without affecting the percentage of twindefects.

Additionally, Comparative Example 5 shows that the desired c/a cannot beachieved, depending on the manufacturing conditions for barium titanatepowder.

TABLE 2 Mean time to failure (minutes) in accelerated Pass/fail inaccelerated longevity longevity test εr Tan δ (%) test [y ≧ {circumflexover ( )}20 × {circumflex over (12 )} (−5)] Example [1] 3,250 3.50% 560◯ Comparative 3,250 7.20% 260 X Example [1] Comparative 3,380 8.50% 130X Example [2] Comparative 2,330 10.50% 100 X Example [3] Example [2]3,370 3.60% 1,200 ◯ Example [3] 3,070 4.50% 2,050 ◯ Example [4] 3,6404.50% 890 ◯ Example [5] 3,280 7.20% 1,040 ◯ Example [6] 2,750 3.50%2,370 ◯ Comparative 3,920 18.50% 70 X Example [4] Comparative 3,56021.00% 85 X Example [5]

In the present disclosure where conditions and/or structures are notspecified, a skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation. Also, in the present disclosureincluding the examples described above, any ranges applied in someembodiments may include or exclude the lower and/or upper endpoints, andany values of variables indicated may refer to precise values orapproximate values and include equivalents, and may refer to average,median, representative, majority, etc. in some embodiments. Further, inthis disclosure, an article “a” or “an” may refer to a species or agenus including multiple species, and “the invention” or “the presentinvention” may refer to at least one of the embodiments or aspectsexplicitly, necessarily, or inherently disclosed herein. In thisdisclosure, any defined meanings do not necessarily exclude ordinary andcustomary meanings in some embodiments.

The present application claims priority to Japanese Patent ApplicationNo. 2012-080788, filed Mar. 30, 2012, the disclosure of which isincorporated herein by reference in its entirety.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

We/I claim:
 1. A ceramic powder that contains, as a main composition,barium titanate powder having a perovskite structure with an averageparticle size (median size) of 200 nm or smaller as measured by SEMobservation, wherein the barium titanate powder is such that thepercentage of barium titanate particles having twin defects in thebarium titanate powder is less than 10% as measured by TEM observationand that its crystal lattice c/a is 1.0075 or more.
 2. A ceramic powderaccording to claim 1, wherein the percentage of barium titanateparticles having twin defects in the barium titanate powder is 5 to 9%.3. A ceramic powder according to claim 1, wherein the crystal latticec/a of the barium titanate powder is 1.0075 to 1.0104.
 4. A ceramicpowder according to claim 2, wherein the crystal lattice c/a of thebarium titanate powder is 1.0075 to 1.0104.
 5. A ceramic powderaccording to claim 1, wherein the average particle size of the bariumtitanate powder is 80 to 150 nm.
 6. A ceramic powder according to claim2, wherein the average particle size of the barium titanate powder is 80to 150 nm.
 7. A ceramic powder according to claim 3, wherein the averageparticle size of the barium titanate powder is 80 to 150 nm.
 8. Aceramic powder according to claim 4, wherein the average particle sizeof the barium titanate powder is 80 to 150 nm.
 9. A multi-layer ceramiccapacitor made by alternately layering a dielectric layer constituted bya sintered body of a ceramic powder according to claim 1, and aninternal electrode layer.
 10. A multi-layer ceramic capacitor made byalternately layering a dielectric layer constituted by a sintered bodyof a ceramic powder according to claim 1, and an internal electrodelayer.
 11. A multi-layer ceramic capacitor made by alternately layeringa dielectric layer constituted by a sintered body of a ceramic powderaccording to claim 2, and an internal electrode layer.
 12. A multi-layerceramic capacitor made by alternately layering a dielectric layerconstituted by a sintered body of a ceramic powder according to claim 3,and an internal electrode layer.
 13. A multi-layer ceramic capacitormade by alternately layering a dielectric layer constituted by asintered body of a ceramic powder according to claim 4, and an internalelectrode layer.
 14. A multi-layer ceramic capacitor made by alternatelylayering a dielectric layer constituted by a sintered body of a ceramicpowder according to claim 5, and an internal electrode layer.
 15. Amulti-layer ceramic capacitor made by alternately layering a dielectriclayer constituted by a sintered body of a ceramic powder according toclaim 6, and an internal electrode layer.
 16. A multi-layer ceramiccapacitor made by alternately layering a dielectric layer constituted bya sintered body of a ceramic powder according to claim 7, and aninternal electrode layer.
 17. A multi-layer ceramic capacitor made byalternately layering a dielectric layer constituted by a sintered bodyof a ceramic powder according to claim 8, and an internal electrodelayer.